Ask a Local
At your first stop, whether you're grabbing a bite to eat or taking a tour, ask a local where their favorite places to eat are. This is one of the best ways to find tasty places to dine.
If you're looking for something spur-of-the-moment, check out what's around you on Google Maps. But make sure you also read the reviews.
Avoid Tacky Tourist Traps
If a restaurant has a large menu, a cheap/tacky interior, or has a gimmick, there's a good chance you're stuck at a tourist trap.
This Wikipedia Hack
From your research, find a dish you've never heard of people and search for the dish in Google Maps. If a restaurant has pictures, definitely check them out.
Restaurants With Plastic Chairs
Plastic chairs may not be catchy, but they are a surprisingly effective way to find the best local restaurants.
Find Popular Places Filled With Locals
Talk to the people that live in the area. Venture outside popular tourist attractions. If you see a busy restaurant and its filed predominantly with locals, check it out!